This invention relates generally to electromagnetic flowmeters, and more particularly to a flangeless flowmeter whose componenets are integrated to form a highly compact, low-cost unit that may be readily installed in a flow line, the unit being compressible between the flanged ends of the upstream and downstream pipes and being capable of withstanding high compressive forces.
Magnetic flowmeters such as those disclosed in U.S. Pat Nos. 3,695,104; 3,824,856; 3,783,687 and 3,965,783, are especially adapted to measure the volumetric flow rates of fluids which present difficult handling problems, such as corrosive acids, sewage and slurries. Because the instrument is free of flow obstructions, it does not tend to plug or foul. The flowmeter can be used to meter liquids without regard to heterogeneous consistency.
An added advantage of an obstructionless construction is that pressure losses are reduced to levels encountered in equivalent lengths of equal diameter pipeline, thereby reducing or conserving pressure source requirements in new or existing hydraulic lines as compared to other metering techniques.
In a magnetic flowmeter, an electromagnetic field is generated whose lines of flux are mutually perpendicular to the longitudinal axis of the flow tube through which the fluid to be metered is conducted and to the transverse axis along which the electrodes are located at diametrically-opposed positions with respect to the tube. The operating principles are based on Faraday's law of induction, which states that the voltage induced across any conductor as it moves at right angles through a magnetic field will be proportional to the velocity of that conductor. The metered fluid effectively constitutes a series of fluid conductors moving through the magnetic field; the more rapid the rate of flow, the greater the instantaneous value of the voltage established at the electrodes.
Typical of commercially-available electromagnetic flowmeters is that unit manufactured by Fischer & Porter Co. of Warminster, Pa., whose Model 10D1430 flowmeter is described in Instruction Bulletin 10D1430A-1-Revision 4. This meter consists of a carbon-steel pipe spool flanged at both ends and serving as a meter body. Saddle-shaped magnetic coils are fitted on opposite sides of the inner surface of the meter body, the magnetically-permeable pipe spool acting as a core or return path for the magnetic field generated by these coils.
The coils in this known form of meter are potted within an epoxy-based compound. An interior liner of neoprene or similar insulating material is inserted within the pipe and turned out against the faces of the mounting flanges. Disposed at diametrically-opposed positions within the central portion of the meter body are two cylindrical electrodes that are insulated from the pipe, the faces of the electrodes being flush with the inner surface of the pipe and coming in contact with the fluid to be metered. Connected to these electrodes and housed in a box external to the pipe are calibration components and a pre-amplifier.
In installing a standard magnetic flowmeter of the above-described type, the meter is interposed between the upstream and downstream pipes of a fluid line, each pipe having an end flanges. The mounting flanges on the meter are bolted to the flanges of line pipes. It is, of course, essential that the circle of bolt holes on the mounting flanges of the meter match those on the pipe flanges.
In a magnetic flowmeter, the flow tube is subjected to the same fluid pressure as the line pipes. The flow tube must therefore be of a material and of a thickness sufficient to withstand this pressure, even though the strength of the flow tube is unrelated to its measuring function. This design factor contributes significantly to the cost of a standard meter. Existing meters of the above-described type which are made up of components that must be assembled are generally of substantial size and weight and quite expensive to manufacture.
In order to provide a compact and readily installable electromagnetic flowmeter whose weight and dimensions are substantially smaller than existing types, the above-identified Schmoock cases, to which the present invention is related, disclose a highly compact flowmeter which, despite its reduced volume and weight, is capable of withstanding high fluid pressures, the flowmeter operating efficiently and reliably to accurately measure flow rates.
The flangeless flowmeter disclosed in said Schmook cases is interposable between the flanged ends of upstream and downstream line pipes for metering fluid passing through the line. In one preferred embodiment, the meter is constituted by a ferromagnetic ring within which a pair of electromagnet coils is supported at opposed positions along a diametrical axis normal to the longitudinal axis of the ring, the longitudinal axis passing through the central flow passage of an annular pressure vessel which is formed of high strength insulating material and is molded within the ring to encapsulate the coils as well as a pair of electrodes disposed at diametrically-opposed positions with respect to the passage along a transverse axis at right angles to the coil axis to define a unitary structure. The unit is compressible between the end flanges of the pipes by bridging bolts that pass through the bore holes in the pressure vessel or which lie outside of the ring to encage the unit.
In the various embodiments of the flowmeter disclosed in the cited Schmook cases, in order to encapsulate the components of the meter with a potting compound, an appropriate mold has to be created for the unit and means must be provided to locate and hold within the mold the various subassemblies, magnet parts and other components of the meter. These requirements complicate the manufacturing procedure and add substantially to the cost of production.
Moreover, since the electronic drive circuit for the electromagnets of the meter and the electronic amplifier, filter networks and other circuits for processing the meter signal which together constitute a converter assembly must be housed in some manner in the proximity of the meter structure, means must therefore be provided to mount the converter assembly on or adjacent to the meter. This requirement introduces a further complication in the installation of the flowmeter in a pipeline.